Field of the Invention
The present invention relates to a display device and a method of driving the same, and more particularly, a display device including a touch panel and a method of driving the same.
Discussion of the Related Art
Touch panels are a type of input device that is included in a display device such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED) and electrophoretic displays (EPDs), and that enables a user to input information by directly touching the screen with a finger, a pen or the like while looking at the screen of the display device.
A touch panel may be manufactured independently from a display panel of a display device, and then may be attached to an upper surface of the display panel or may be provided as one body integrated with the display panel.
For example, a touch panel may be categorized into an in-cell type in which the touch panel is built into the pixels of the display panel, an on-cell type in which the touch panel is provided on the display panel, and an add-on type in which the touch panel is manufactured independently from the display panel and is then attached to an upper end of the panel.
Recently, the in-cell type touch panel has been receiving attention due to its aesthetic design and slimness. That is, the demand for a display device including such an in-cell type touch panel, in which various elements of the touch panel are built into the display panel, is increasing for slim and portable terminals such as smart phones and tablet personal computers (PCs)
FIG. 1 is an exemplary diagram for describing a method of driving a touch panel according to the related art, and FIG. 2 is a waveform diagram showing an image display period and a touch sensing period in an in-cell type display device according to the related art.
A touch panel is for sensing a user's touch, and may be implemented in various types such as a resistive type and a capacitance type. Hereinafter, a touch panel using the capacitance type will be described with reference to FIG. 1.
Referring to FIG. 1, the touch panel 40 is an in-cell type touch panel, and includes a plurality of driving electrodes 21 for supplying driving voltages. The touch panel 40 further includes a plurality of receiving electrodes 11, which are typically formed in parallel with a plurality of gate lines formed in the display panel into which the touch panel 40 is integrated, for transferring a plurality of sensing signals generated by the driving voltages to a touch sensing unit 60. The touch sensing unit 60 includes a driver 62 for supplying the driving voltages to the driving electrodes 21 and a receiver 61 for determining whether the touch panel 40 is touched by using the sensing signals received from the receiving electrodes 11.
In the display device including the touch panel 40 according to the related art, in order to determine whether the touch panel 40 is touched, the driving voltage is sequentially supplied to the driving electrodes 21, and the sensing signals are received from all the receiving electrodes 11 while the driving voltage is sequentially applied to the driving electrodes 21.
The sensing signal contains information on a change in capacitance that is generated between the driving electrode 21 driven with the driving voltage and the receiving electrode 11, and the touch sensing unit 60 analyzes the change in capacitance to determine whether the touch panel 40 is touched.
In an in-cell type display device, the driving electrodes 21 and the receiving electrodes 11 also functions as a common electrode which is formed in a pixel of the display panel and are supplied with a common voltage.
During an image display period, the driving electrodes 21 and the receiving electrodes 11 perform a function of the common electrode of the pixel driven with the common voltage. Also, during a touch sensing period, the touch sensing unit 60 supplies the driving voltage to the driving electrodes 21, and determines whether the touch panel is touched, by using the sensing signals received from the receiving electrodes 11.
To do so, as shown in FIG. 2, a period of one frame is, for example, divided into the image display period and the touch sensing period.
During the image display period, the common voltage is supplied to the driving electrodes 21 and the receiving electrodes 11. During the touch sensing period, a pulse-type driving voltage is supplied to the driving electrodes 21, and the sensing signals are transferred from the receiving electrodes 11 to the touch sensing unit 60.
When the number of the driving electrodes 21 is p and the number of the receiving electrodes 11 is q, the touch sensing unit 60 receives q number of sensing signals from the q receiving electrodes 11 and analyzes the received sensing signals during the touch sensing period.
The driving electrodes 21 and the receiving electrodes 11 are typically formed on the same plane, with a short distance between adjacent electrodes, which increases the change in capacitance generated between the driving electrodes 21 and the receiving electrodes 11.
The touch panel 40 is typically applied to small electronic devices such as smartphones, tablet personal computers (PCs), notebook computers, monitors, etc. As a result, a parasitic capacitance in the touch panel 40 may not greatly affect the sensing performance.
However, when the touch panel 40 is applied to large-sized display devices such as large televisions (TVs), large monitors, and electronic bulletin boards, the number of parasitic capacitors may increase exponentially, and thus, the parasitic capacitance increases at the same time. When the parasitic capacitance increases, a load of the receiving electrodes 11 increases, and for this reason, the sensing performance of the touch sensing unit 60 is degraded. That is, when the in-cell type touch panel according to the related art is applied to a large-size display device, the load of the receiving electrodes 11 increases due to the parasitic capacitance, and for this reason, the sensing performance of the touch sensing unit 60 is degraded.
Moreover, the in-cell type touch panel 40 according to the related art uses a differential driving method that compares the plurality of sensing signals received from two receiving electrodes, which are formed in parallel with the gate lines, to determine whether one of the two receiving electrodes is touched. However, as shown in FIG. 1, when the lowermost receiving electrode A, which is formed at a lowermost portion of the touch panel 40 among the receiving electrodes, is touched, there is no receiving electrode to be used for comparison with the lowermost receiving electrode A. In order to determine whether the lowermost receiving electrode A is touched, either a virtual sensing signal or a sensing signal received from the uppermost receiving electrode A, which is formed at a position opposite to the lowermost receiving electrode A, is used. In such cases, the determination of a touch on the lowermost driving electrode A may be inaccurate.